Modern automated theatrical spotlights are capable of projecting images and patterns of light onto a stage area and its scenic elements to create textures and effects which enhance the staged production. The origin of these patterns are usually small glass disks having the imagery encoded into a metalized or other coating on one side of the glass. These patterned disks are known as gobos in the lighting industry. The gobos are typically mounted in holders that are then fitted around the periphery of a motorized wheel allowing the lighting system operator to select one pattern for projection from the multiple images available on the wheel. The gobo patterns may be abstract silhouette patterns, gray scale photorealistic images or colored patterns and images.
In advanced automated luminaires, and in order to further enhance the gobo effect, gobo holders may be made with gear teeth which are then individually mounted in bearings. This allows the patterns to be rotated to a particular orientation or spun continuously at a given speed. This rotational control allows the operator to orient a corporate logo for example, to a specific angle for projection or to continuously rotate a projected pattern providing a dynamic effect on a backdrop or on the stage floor. This rotational control may be provided by a second motorized system that has a central sun gear rotationally mounted at the center of the gobo wheel such as described in our application Ser. No. 11/777,006. The sun is rotationally connected to the individual planet gobos by meshing gear teeth. When the sun gear is rotated by its driving motor, all of the planet gobos mounted on the wheel rotate concomitantly. Such a system is known as a rotating gobo mechanism.
The extent of projected effects may be further enhanced if the automated luminaire is fitted with two or more rotating gobo wheels. When two gobo images on separate wheels are aligned along the optical path in the light beam, the operator may change focus using the projection lens. At one time, the operator causes the focus to be on the first image. The operator then commands the lens to slowly move so that the focus shifts to the second image. The effect is such that the first image gradually morphs or dissolves into the second providing a smooth and pleasant change.
Modern theatrical projection systems employ fast projection lens systems which are required in order to deliver high light intensity levels to the stage. Fast lenses, described as having a low f-number, inherently have a shallow depth of focus. Therefore, the images of gobos mounted on two different wheels cannot be in focus at the same time. Only objects occupying essentially the same plane may be projected in focus together. This limitation prevents the operator from projecting two focused and overlapping images which is a desirable effect.